Technical Abstract:
Sclerotinia minor is the causal agent of Sclerotinia blight, a disease that significantly reduces peanut (Arachis hypogea) productivity. This study analyzed the diversity and population structure of 164 S. minor isolates from Oklahoma. Isolates were obtained from infected stems of peanut plants from four lots at the Oklahoma Agricultural Experiment Station. Isolates used for Sclerotinia blight resistance screening in peanuts, collected between 1981 and 1993, were also included in the analysis. Inter Simple Sequence Repeat (ISSR) fingerprinting was used for evaluation of the population structure and genetic diversity of the S. minor sample. Of a total of 50 fragments amplified, 38 were polymorphic (76%). AMOVA identified significant genetic differences within the sample (PHI PT = 0,091; p = 0,001), of which 9.1% of the genetic variation exist between lots and the other 90.9% is distributed within lots. Nei's genetic distance, GST, and PCO revealed close relationships between the populations from lots used for peanut breeding and isolates used for disease resistance screenings, with little although significant differentiation between plots. However, isolates collected from chemical testing plots were significantly different from all the others. Our results confirmed the validity of the current isolate panel for peanut germplasm Sclerotinia blight resistance screening. New S. minor genotypes were identified that could be of value for peanut breeding programs in the future.